The use of combing wheel feed means to feed cut sheets to an open feed nip associated with a printer is well known; U.S. Pat. No. 640,368 is an example.
The problem of second sheet restraint, or restraint of the shingled sheets under the top sheet, has been addressed previously. For example, the above-mentioned U.S. Patent uses a hold-down device at the back of the sheet stack.
U.S. Pat. No. 868,317 suggests the use of a ramp and an air blast at the front of the stack to minimize multiple sheet feed, whereas U.S. Pat. No. 939,182 suggests the use of a ramp.
U.S. Pat. No. 1,986,558 suggests the use of a fulcrum foot, at the location of the combing wheel, which is lowered onto the stack as the combing wheel is raised.
As this prior art suggests, combing wheels are conventionally operable to shingle the leading edge of the top (or bottom) sheet of a stack into an open drive nip. The closing of this nip is operable to feed the sheet away from the stack, whereas the combing wheel is the means whereby only one sheet is staged into this open drive nip.
The present invention provides a unique drive nip closing member, constructed and arranged to inhibit second sheet feeding, and to preserve the shingled state of the second and its underlying sheets.
Specifically, the present invention's nip closing member includes a movable soft or resilient foam rubber pad which imprisons the leading edges of the second and its underlying sheets in a manner to prevent these sheets from moving in a sheet feeding direction with the top sheet (due to intersheet friction), and yet this pad does not push these sheets back toward the stack.
More specifically, the drive nip of the present invention is closed by a composite pad including a hard, low friction pad, and the above-mentioned foam rubber pad. The low friction material pushes the top sheet onto a continuously rotating feed roller, causing this sheet to be fed to the copier's transfer station. This low friction pressure pad is thicker than the upstream-located foam pad. Thus, a second-sheet-stop or step is formed. If the second sheet tends to feed with the top sheet, due to intersheet friction, it moves only so far as this step. In fact, sheets under the top sheet may not move at all due to the retarding effect of the soft foam pad. In any event, movement of these sheets, and specifically the sheet directly under the top sheet, is positively limited by the step. In like manner, the foam pad resists movement of all underlying sheets, due to intersheet friction.
As a further feature of the present invention, a spring biases the top sheet, and its underlying shingled sheets away from the feed roller, and specifically biases the leading edge of the second and its underlying sheets into the soft foam pad when the drive nip is closed.